1. Field of the Invention
The present invention relates to an information processing apparatus connected to an image processing apparatus that corrects colors in an image output from a printer, an information processing method, and a storage medium.
2. Description of the Related Art
Recently, devices that realize the same level of image quality as printing devices have appeared along with improvements in the performance of electrophotographic image processing apparatuses (hereinafter referred to as image processing apparatuses). However, fluctuations in density and color are greater in such devices as compared to the printing devices due to instability unique to the electrophotographic method.
To solve such a problem, the conventional image processing apparatus includes a single color calibration technique. The single calibration technique generates a look up table (LUT) for correcting one-dimensional gradation characteristics corresponding to each of cyan, magenta, yellow, and black (C, M, Y, and K) toners. The LUT is a table indicating output data corresponding to input data segmented at specific intervals, capable of expressing a non-linear characteristic that cannot be expressed by an arithmetic expression.
A one-dimensional LUT for correcting the density is a table indicating output signal values corresponding to each of C, M, Y, and K input signal values, and the image processing apparatus forms the image on a sheet of paper using amounts of toner according to the output signals.
When the image processing apparatus generates the one-dimensional LUT, a chart configured by patches of data having different gradations corresponding to each of the C, M, Y, and K toners is provided. The chart is output from the image processing apparatus.
The chart is then measured using a sensor or a scanner arranged in the image processing apparatus, or a color measurement device (i.e., a colorimeter) other than the image processing apparatus. The measured value is compared with preset target data, so that the one-dimensional LUT (1D-LUT) for correcting each of the C, M, Y, and K colors independently is generated. The “single color” indicates a color expressed using a single toner, i.e., C, M, Y, or K.
Further, in recent years, there is a technique for performing calibration of mixed colors using a four-dimensional LUT (4D-LUT) (refer to Japanese Patent Application Laid-Open No. 2011-254350). The mixed color indicate red, green, blue, or a color formed using a plurality of toners, such as gray formed using C, M and Y toners. The 4D-LUT converts a combination of the signal values for outputting each of the C, M, Y, and K toners to a different combination of the C, M, Y, and K signal values.
A non-linear difference often occurs with respect to the mixed color in the image processing apparatus even when the gradation characteristics of a single color is corrected using the 1D-LUT. The mixed colors, i.e., colors formed using a plurality of toners, can thus be corrected employing the 4D-LUT.
The process for performing calibration in the case where the mixed color is included will be described below. A patch is output to a recording medium such as a sheet, employing the chart data used in single color calibration, for performing the single color calibration. The patch is then read by the scanner or the sensor. The data acquired by reading the patch is compared with a preset target value, and the 1D-LUT for correcting the difference from the target value is generated. A patch is then output to the recording medium employing mixed color chart data converted by the previously generated 1D-LUT, for performing the mixed color calibration. The patch is then read by the scanner or the sensor. The data acquired by reading the patch is compared with the preset target value, and the 4D-LUT for correcting the difference from the target value is generated.
As described above, the mixed color characteristics that cannot be corrected by only performing the single color calibration can be corrected with high accuracy by performing the mixed color calibration.
Furthermore, recent image processing apparatuses include a plurality of paper feed stages for storing the sheets to be printed on. Each of the paper feed stages store various types of sheets having different grammage, size, surface texture, and chromaticity, for generating printed products having various values. In particular, the grammage and the surface texture of the sheet and the chromaticity the sheet itself are closely related to the gradation characteristics and reproduction of the mixed color characteristics to be corrected by performing calibration. It is thus important that each LUT and the paper type are associated with each other to assure that the image quality is appropriately corrected. In other words, the paper type and the target value of the calibration are associated with each other, and the target value changes along with the paper type. More specifically, if the grammage and the surface texture of the sheet and the chromaticity the sheet itself are different, the density and the mixed color become different even when the same toners are fixed on the sheet.
To solve such a problem, Japanese Patent Application Laid-Open No. 2011-43815 discusses a technique for indicating, when performing calibration, the paper feed stage storing the sheet to be used in performing calibration.
However, according to Japanese Patent Application Laid-Open No. 2011-43815, the paper feed stage storing the sheet used when performing the appropriate single color calibration or the mixed color calibration cannot be confirmed after performing calibration or when performing printing. As a result, the image processing apparatus may perform printing using a sheet on which an appropriate calibration table has not been generated, even when the image processing apparatus has generated the appropriate calibration table for another sheet. In such a case, the printed product in which the gradation characteristics and the mixed color characteristics are inappropriate is output.